The present research is first to investigate the unique effect of a humorous clown intervention on patients’ emotional state in comparison with a different kind of intervention in a hospital setting using a controlled experimental method. Forty-four adult patients of a physical rehabilitation center were randomly assigned to either participate or observe 2 interventions: a hospital clown and a nurse intervention. Compared with baseline and the nurse intervention, the clown intervention elicited a higher level of amusement in patients. Both interventions elicited arousal, and neither intervention led to a change in negative emotions. No difference was found between the emotional states of participants and observers of the interventions at any level. A combination of general funniness of clown performances and felt transcendence during the hospital clown intervention best predicted the total amount of positive affect experienced during the intervention, which supports and extends results from previous studies. The results clearly support the benefit of hospital clown interventions for the elicitation of a positive emotional state in patients. Clowns working in hospitals should be encouraged to continue their work with patients in need of care.